The overall goal of this project is to try to understand how the neuronal spectrin cytoskeleton organizes postsynaptic receptors in glutaminergic neurons, stabilizes the neuronal membrane, and is altered by gp120 and excitatory amino acids (EAA). Specifically, the work will focus on the factors which sort unique isoforms of spectrin, protein 4.1, ankyrin, and adducin to the postsynaptic membrane, and regulate the interactions between these proteins and other components of the neural membrane. Neuron specific components of interest include the putative non CD4 gp120 receptor and the NMDA receptor. Regulatory events acting on the spectrin skeleton to be examined include calpain-I mediated proteolysis, Ca++ and calmodulin, and phosphorylation by cAMP-dependent and independent kinases, calmodulin kinesis, and protein kinase C. The distribution of unique isoforms and of post-translationally modified proteins will be identified in normal and AIDS patient's brains by immunofluorescent and immuno-electron microscopy using monoclonal and sequence-specific antibodies. Interactions between purified or recombinant protein components will be characterized by in vitro assay in cultured neuronal cells. The rate of incorporation of these protein components into the neuronal cytoskeleton, and post-translational modification after EAA or recombinant gp120 stimulation, will also be followed. The applicant proposes to identify functional sites in spectrin critical for in vivo assembly at the neuronal membrane or for (functional) linkage to gp120 or NMDA receptors. He will try to identify them by the ability of expressed recombinant wild-type and mutated proteins to associate with membranes in cultured neuronal cells and be post-translationally modified following receptor activation.